1. Field of the Invention
The present invention relates generally to stationary combustion turbines and, more particularly, is concerned with a catalytic combustor employing an arrangement of catalyzed and non-catalyzed substrate passages for providing passive cooling of the catalytic combustor.
2. Description of the Prior Art
In the operation of a conventional combustion turbine, intake air from the atmosphere is compressed and heated by rotary action of a multi-vaned compressor component and caused to flow to a plurality of combustor components where fuel is mixed with the compressed air and the mixture ignited and burned. The heat energy thus released then flows in the combustion gases to the turbine component where it is converted into rotary energy for driving equipment, such as for generating electrical power or for running industrial processes. The combustion gases are finally exhaused from the turbine component back to the atmosphere.
Various schemes have been explored to adapt combustion turbines for the aforementioned uses without exceeding NO.sub.X emission limits. The use of catalytic combustion is a promising approach because it can occur at about 2300 to 2500 degrees F to produce a high turbine inlet temperature for turbine operating efficiency without any significant side effect NO.sub.X generation from reactions between nitrogen and oxygen which occurs at temperatures over 3000 degrees F. In contrast, conventional flame combustion at about 4500 degrees F results in NO.sub.X generation which typically exceeds the limits set in more restrictive areas such as California.
Representative of prior art catalytic combustor arrangements for use with a combustion turbine are those disclosed in U.S. Pat. Nos. to Pfefferle (3,846,979 and 3,928,961), DeCorso et al (3,938,326 and 3,943,705), Mosier et al (4,040,252), Sanday (4,072,007), Pillsbury et al (4,112,675), Shaw et al (4,285,192), and Scheihing et al (4,413,470); and Canadian Patent Nos. 1,070,127, 1,169,257 and 1,179,157.
In a typical catalytic combustor, such as disclosed in U.S. Pat. No. 4,413,470 and Canadian Patent No. 1,169,257, active catalysts being supported (i.e. coated) on various substrates (e.g. ceramic honeycomb structures) provide an effective means of initiating and stabilizing the combustion process when they are used with suitable mixtures of fuel and air. These combustion catalysts have several desirable characteristics: they are capable of minimizing NO.sub.X emission and improving the pattern factor. However, one of their limitations is that their maximum operating temperature tends to be only marginally acceptable as an turbine inlet temperature.
This limitation is inherent in the way the typical catalytic combustor operates. Catalysts initiate the combustion reaction at their surfaces and at temperatures lower than normal ignition temperature. However, once the reaction is initiated, it continues in the gas stream and persists beyond the catalyst in the form of afterburning. Simultaneously, the catalyst substrate temperature increases, resulting in an accelerated reaction which moves the reaction zone further upstream in the catalyst. The result may be damage of the catalyst and/or catalyst substrate if the fuel/air ratio is such as to give an excessive catalyst outlet temperature. Presently available catalysts have the capability of extended operation at about 2289 degrees F (1527 degrees K). However, a turbine inlet temperature of around 2500 degrees F is desired. Thus, given the aforementioned current catalyst temperature limits, the catalyst is clearly incapable of providing such turbine inlet temperature.
Consequently, a need exists for a technique to achieve a higher catalyst operating temperature requirements without damaging the catalyst.